Exhaust driven turbochargers for vehicle engines are well known. A turbine of the turbocharger driven by exhaust gas, drives a compressor on the inlet side, and thereby increases the charge volume of each combustion cycle of the engine.
Also known is the technique of exhaust gas recirculation (EGR), whereby exhaust gas is re-circulated to the inlet side of the engine to dilute the fresh air charge during a cold engine start for the purpose of reducing noxious emissions.
High pressure EGR provides exhaust gas from at or adjacent the exhaust manifold. This arrangement is somewhat disadvantageous since the exhaust gas stream is hot, and thereby increases the temperature of the inlet charge upon mixing therewith. Also such exhaust gas is unfiltered, and thus contains carbon and other contaminants which may cause deterioration of engine lubricant.
So-called low pressure EGR is an alternative which provides exhaust gas from a point in the exhaust system downstream of the usual diesel oxidation catalyst (DOC) and diesel particle filter (DPF). Such gas is relatively cool and clean, but is substantially at tail pipe pressure. The consequence of relatively low pressure is that insufficient volume may flow, or be drawn, into the engine inlet tract. A pump may thus be provided to ensure that a sufficient volume of relatively cool and clean exhaust gas can be provided to the inlet tract on demand.